The present invention relates to the field of microwave thermal therapy of tissue. In particular, the present invention relates to a catheter for transurethral microwave thermal therapy of benign prostatic hyperplasia (BPH).
The prostate gland is a complex, chestnut-shaped organ which encircles the urethra immediately below the bladder. Nearly one third of the prostate tissue anterior to the urethra consists of fibromuscular tissue that is anatomically and functionally related to the urethra and bladder. The remaining two thirds of the prostate is generally posterior to the urethra and is comprised of glandular tissue.
This relatively small organ, which is the most frequently diseased of all internal organs, is the site of a common affliction amonq older son: BPH (benign prostatic hyperplasia). BPH is a nonmalignant, bilateral nodular expansion of prostrate tissue in the transition zone, a periurethral region of the prostate between the fibromuscular tissue and the glandular tissue. The degree of nodular expansion within the transition zone tends to be greatest anterior and lateral to the urethra, relative to the posterior-most region of the urethra. Left untreated, BPH causes obstruction of the urethra which usually results in increased urinary frequency, urgency, incontinence, nocturia and slow or interrupted urinary stream. BPH may also result in more severe complications, such as urinary tract infection, acute urinary retention, hydronephrosis and uraemia.
Traditionally, the most frequent treatment for BPH has been surgery (transurethral resection). Surgery, however, is often not an available method of treatment for a variety of reasons. First, due to the advanced age of many patients with BPH, other health problems, such as cardiovascular disease, can warrant against surgical intervention. Second, potential complications associated with transurethral surgery, such as hemorrhage, anesthetic complications, urinary infection, dysuria, incontinence and retrograde ejaculation, can adversely affect a patient's willingness to undergo such a procedure.
A fairly recent alternative treatment method for BPH involves microwave thermal therapy, in which microwave energy is employed to elevate the temperature of tissue surrounding the prostatic urethra above about 45.degree. C., thereby thermally damaging the tusorous tissue. Delivery of microwave energy to tumorous prostatic tissue is generally accomplished by a microwave antenna-containing applicator, which is positioned within a body cavity adjacent the prostate gland. The microwave antenna, when energized, heats adjacent tissue due to molecular excitation and generates a cylindrically symmetrical radiation pattern which encompasses and necroses the tumorous prostatic tissue. The necrosed intraprostatic tissue is subsequently reabsorbed by the body, thereby relieving an individual from the symptoms of BPH.
One method of microwave thermal therapy described in the art includes intrarectal insertion of a microwave antenna-containing applicator. Heat generated by the antenna's electromagnetic field is monitored by a sensor, which is positioned near the prostate gland by a urethral catheter. Owing to the distance between the rectum and the tumorous prostatic tissue of the transition zone, however, healthy intervening tissue within the cylindrically symmetrical radiation pattern is also damaged in the course of the intrarectal treatment. Intrarectal microwave thermal therapy applicators are described in the following references: Eshel at al. U.S. Pat. No. 4,813,429; and, A. Yerushalmi et al., Localized Dean Microwave Hyperthermia in the Treatment of Poor Operative Risk Patients with Benign Prostatic Hyperplasia, 133 JOURNAL OF UROLOGY 873 (1985).
A safer and more efficacious treatment of BPH is transurethral microwave thermal therapy. This method of treatment minimizes the distance between a microwave antenna-containing applicator and the transition zone of the prostate by positioning a Foley-type catheter-bearing applicator adjacent to the prostate gland within the urethra. Due to the close proximity of the microwave antenna to the prostate, a lessor volume of tissue is exposed to the cylindrically symmetrical radiation pattern generated by the microwave antenna, and the amount of healthy tissue necrosed is reduced. Intraurethral applicators of the type described can be found in Turner et al. U.S. Pat. No. 4,967,765 and Hascoet et al. European Patent Application 89403199.6.
While the close proximity of a transurethral microwave thermal therapy applicator to prostatic tissue reduces the amount of damage to healthy tissue, controlling the volume of tissue to be affected by the microwave energy field continues to be problematic. For instance, microwave antennas known in the art have tended to produce electromagnetic fields which affect a volume of tissue, beyond the desired area of treatment, which necroses healthy, normal tissue.